1. Field of the Invention
The present invention relates generally to the field of wet chemical processing, and more specifically to an apparatus for controlling wafer rinse water from entering an electrofill chemical bath.
2. Description of Related Art
Machines for cleaning and processing wafers in the electronics industry are generally well known. Conventional processes involve plating a metal layer on a semiconductor wafer surface using a plating apparatus. One goal of wafer plating is to uniformly fill the holes and trenches with a conductive material. Thin film plating of copper into sub-micron holes and trenches has become more difficult in ULSI chip processing, particularly when the feature size is below 0.25 μm. In the field of chemical processing, and chemical plating in particular, it is important that the composition and concentration of various constituents be controllable. This includes the integrity and consistency of the chemical bath constituents and concentrations used for plating. After each processing step, it is often desirable to thoroughly clean, rinse, and dry the workpiece to ensure that debris is removed from the workpiece. Thus, methods and apparatus for cleaning, rinsing, and drying wafers have been made available in the art to minimize wafer damage and process degradation. For example, in a wet chemical deposition process, after a substrate is treated with chemicals, it is rinsed, generally in a de-ionized water spray although other post-treatments are used, such that the chemicals are washed off the substrate by the spray shower. Conventionally, in a wet process of semiconductor fabrication where the de-ionized water spray rinse is performed in the same tool as the chemical bath, this causes the problem of diluting the chemical bath with excess water runoff. In an electrofill tool, a wafer is generally placed into copper-acid bath chemistry where copper is plated to the wafer surface using electric current. The need to rinse wet chemical fluids is unique to the electrolytic process. Both before and after a plating process, the wafer surface is rinsed with water in the same tool where the chemical bath is the lowest chamber. If too much of this water enters the copper-acid bath, it will cause dilution of the chemistry, which must be controlled tightly to maintain uniform plating. Similarly, a sulfuric acid bath is sometimes used to remove organics from the wafer. Again, rinsing the wafer in a chamber above a sulfuric acid bath would dilute the acid bath. Thus, a portion of the rinse needs to be deflected from the bath in order to maintain the bath's original chemical concentration. Furthermore, since there are at least two steps in a deposition process to introduce de-ionized water, pre- and post-treatments, there are at least two opportunities for dilution, which must be mitigated. Generally, a pre-rinse limits impurities and defects from forming on the deposition surface, and a post-rinse, performed after deposition, decreases the corrosive effect on the wafer.
The present invention contemplates a device for shielding the chemical bath from dilution during the rinse process steps in an electrofill tool where the rinsing occurs in the same apparatus as the plating.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an apparatus for limiting the dilution of a chemical bath due to rinse washes on wafers in an electrofill tool.
It is another object of the present invention to provide an apparatus for controlling the chemistry of a chemical bath.
A further object of the invention is to provide an apparatus that maintains uniform plating chemistry during electrofill deposition.
It is yet another object of the present invention to provide an apparatus to facilitate pre- and post-rinses during wet-chemistry deposition.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.